閉鎖性内湾における光合成硫黄細菌由来有機物の高次捕食者への転送に関する基礎的研究閉鎖性内湾における光合成硫黄細菌由来有機物の高次捕食者への転送に関する基礎的研究The transfer of photosynthetic sulfur bacteria-derived organic matter to the organisms at a higher trophic level at a semi-closed bay

Hypoxic water mass often formed in semi-closed bay during summer causes mass death events of the benthic organisms due to anoxic water at the bottom layer. On the other hand, autotrophic bacteria which proliferate in the anoxic condition may partially contribute to biological production in the bay, as food source for the heterotrophs inhabiting outside the hypoxic water mass. In this study, we
investigated whether the organic matter derived from photosynthetic sulfur bacteria, a species of anaerobic autotrophic bacteria which were incubated from the bottom sediment in the Omura Bay, were actually assimilated by benthic filter feeders, based on the stable isotopes (13C, 15N)-labeled techniques. First, 13C, 15N-labeled bacteria were fed to a bivalve, Anadara broughtonii. And carbon (C) and nitrogen (N)
assimilation rates were determined, and compared with the results from the control experiments in which labeled phytoplankton were fed. The assimilations of bacteria-derived organic C and N into the muscle tissue in A. broughtonii were surely confirmed, although the assimilation rates were greatly smaller than those of phytoplankton-derived organic matter (i.e., 1/36 for C, 1/6 for N). The lower
assimilation rate of C compared with N in either of the food sources (i.e., 50% in case of phytoplankton, and 10% bacteria) suggested that newly incorporated C was promptly metabolized as respiratory
substrate. The results of this study suggested that an increase in the biomass of anaerobic autotrophic bacteria associated with hypoxic water mass contributes to biological production in the inner bay as
one of food sources.